1. Field of the Invention
The present invention relates to an alternator driven by an internal combustion engine, for example, and in particular, relates to a stator construction for an automotive alternator mounted to an automotive vehicle such as a passenger car or a truck.
2. Description of the Related Art
FIG. 18 is a side elevation showing part of a stator of a conventional automotive alternator such as described in Japanese Patent No. 2927288, for example, FIG. 19 is a perspective showing a conductor segment used in the stator of the conventional automotive alternator shown in FIG. 18, and FIGS. 20 and 21 are perspectives from a front end and a rear end, respectively, of part of the stator of the conventional automotive alternator shown in FIG. 18.
In FIGS. 18 to 21, the stator 50 includes: a stator core 51; a stator coil 52 wound into the stator core 51; and insulators 53 mounted inside slots 51a, the insulators 53 insulating the stator coil 52 from the stator core 51. The stator core 51 is a cylindrical laminated core laminated by stacking thin steel plates, and has a number of slots 51a extending axially disposed at even pitch circumferentially so as to be open on an inner circumferential side. The stator coil 52 is constructed by joining a number of short conductor segments 54 in two three-phase coils. In this case, ninety-six slots 51a are formed so as to house two three-phase coils such that the number of slots housing each phase of the winding portions corresponds to the number of magnetic poles (sixteen) in a rotor (not shown). The two three-phase coils have a mutual phase difference of 30xc2x0 (electrical angle).
The conductor segments 54 are formed into a general U shape from an insulated copper wire material having a rectangular cross section, and are inserted two at a time from an axial rear end into pairs of slots 51a six slots apart (a pitch of one magnetic pole). Then, end portions of the conductor segments 54 extending outwards at a front end are joined to each other to constitute the stator coil 52.
More specifically, in pairs of slots 15a six slots apart, first conductor segments 54 are inserted from the rear end into first positions from an outer circumferential side within first slots 51a and into second positions from the outer circumferential side within second slots 51a, and second conductor segments 54 are inserted from the rear end into third positions from the outer circumferential side within the first slots 51a and into fourth positions from the outer circumferential side within the second slots 51a. Thus, within each slot 15a, four straight portions 54a of the conductor segments 54 are arranged to line up in a row in a radial direction.
Then, end portions 54b of the conductor segments 54 extending outwards at the front end from the first positions from the outer circumferential side within the first slots 51a and end portions 54b of the conductor segments 54 extending outwards at the front end from the second positions from the outer circumferential side within the second slots 51a six slots away in a clockwise direction from the first slots 51a are joined to form an outer layer winding having two turns. In addition, end portions 54b of the conductor segments 54 extending outwards at the front end from the third positions from the outer circumferential side within the first slots 51a and end portions 54b of the conductor segments 54 extending outwards at the front end from the fourth positions from the outer circumferential side within the second slots 51a six slots away in a clockwise direction from the first slots 51a are joined to form an inner layer winding having two turns.
In addition, the inner layer winding and outer layer winding constituted by the conductor segments 54 inserted into the pairs of slots 51a six slots apart are connected in series to form one coil phase having four turns.
A total of six coil phases each having four turns are formed in this manner. The two three-phase coils constituting the stator coil 52 are formed by connecting three coil phases each into alternating-current connections.
In the conventional stator 50 constructed in this manner, at the rear end of the stator core 51, turn portions 54c of the pairs of conductor segments 54 inserted into the same pairs of slots 15a are lined up in rows in a radial direction. As a result, the turn portions 54c are arranged in two rows circumferentially to constitute a rear-end coil end group.
At the front end of the stator core 51, on the other hand, joint portions formed by joining the end portions 54b of the conductor segments 54 extending outwards at the front end from the first positions from the outer circumferential side within the first slots 51a and the end portions 54b of the conductor segments 54 extending outwards at the front end from the second positions from the outer circumferential side within the second slots 51a six slots away, and joint portions formed by joining the end portions 54b of the conductor segments 54 extending outwards at the front end from the third positions from the outer circumferential side within the first slots 51a and the end portions 54b of the conductor segments 54 extending outwards at the front end from the fourth positions from the outer circumferential side within the second slots 51a six slots away are arranged to line up radially. As a result, joint portions formed by joining end portions 54b to each other are arranged in two rows circumferentially to constitute a front-end coil end group.
In the stator 50 of the conventional automotive alternator, as explained above, the stator coil 52 is constructed by inserting short conductor segments 54 formed in the general U shape into the slots 51a of the stator core 51 from the rear end, and joining end portions 54b of the conductor segments 54 extending outwards at the front end. The end portions 54b of the conductor segments 54 are joined to each other by clamping a portion thereof in a jig, and soldering or welding the tips thereof.
Now, the coil end leakage reactance due to leakage of the magnetic flux passing through the coil ends is proportionate to the height of the coil ends. In the conventional stator coil 52, because clamping area is required for the jig, making the coil ends high, there has been a problem of increased coil end leakage reactance, causing output to deteriorate.
Furthermore, if the number of claw-shaped magnetic poles and the number of slots are increased, the coils in the coil ends are closer together, and when the joining portions of the conductor segments expand, because the space between the coils in the coil ends become excessively narrow and the height of the coil ends is increased, there is mutual interference between the coils in the coil ends, and there has been a problem of deterioration in output.
Furthermore, in the conventional stator 50, a large number of the short conductor segments 54 must be inserted into the stator core 51 and their end portions 54b must be joined by welding, soldering, etc., which has led to a problem of significantly decreased operability. In addition, when joining the end portions 54b, there has also been a problem of short circuiting often occurring between the joint portions due to spilt solder or weld melt, significantly decreasing mass-productivity.
Furthermore, in the conventional stator construction which uses conductor segments 54, because buckling, etc., occurs more frequently during insertion of the conductor segments 54 into the slots as the number of slots increases, it has been difficult to apply this construction to an alternator aiming for compactness and high output by increasing the number of claw-shaped magnetic poles and the number of slots.
Furthermore, there has been a problem of decreased reliability of the conventional stator 50 constructed in this manner because of the problems explained below.
First, because the front-end coil end groups are constructed such that the joint portions between the end portions 54b where the insulation coating has been lost due to welding and soldering are arranged in rows in a circumferential direction, the coil-end construction becomes susceptible to corrosion through exposure to moisture and the ability to withstand corrosion is extremely low.
Furthermore, because the coil ends are constructed from ninety-six joining portions in two rows, that is from 192 joining portions, the construction is susceptible to short circuiting, and short-circuiting accidents happen easily.
In addition, because the amount of the conductor segments 54 which must be pushed through the slots 51a must be greater than the axial length of the stator core 51, the insulation coating of the conductor segments 54 is easily damaged.
Furthermore, the conventional stator 50 aims to reduce magnetic noise by mutually canceling out magnetic pulation forces by winding into the slots two three-phase coils which are offset in positions having an electrical phase difference of 30. However, in this construction, although the fifth and seventh magnetomotive harmonic frequencies of the stator can be reduced, one problem has been that the eleventh and thirteenth magnetomotive harmonic frequencies of the stator, which occupy a large ratio among the magnetic flux pulsation which arise in the alternator, are increased, decreasing the effective reduction in magnetic noise. In addition, because the end portions 54b of the conductor segments 54 are welded together, softening occurs in the conductor segments 54 due to the rise in temperature during welding, reducing the rigidity of the stator and decreasing the effective reduction in magnetic noise.
Furthermore, if the number of claw-shaped magnetic poles and the number of slots are increased in order to achieve compactness and high output, pulsation in magnetic flux occurring between the teeth and the claw-shaped magnetic poles increase, and at the same time because the rigidity of the stator is decreased by the reduction in the width of the teeth, magnetic noise tends to be promoted. Consequently, with the magnetic counter-measures in which two three-phase coils are wound into the slots such that their positions are offset by an electrical phase difference of 30xc2x0, another problem has been that it is not possible to sufficiently reduce magnetic noise in an alternator achieving compactness and high output.
The present invention aims to solve the above problems, and an object of the present invention is to provide an alternator enabling the achievement of high output, increased reliability, and improved productivity by constructing a stator coil with a number of winding sub-portions composed of continuous wire, thereby reducing coil end height and reducing the number of coil-end joining portions.
An additional object of the present invention is to provide an alternator capable of achieving a reduced level of noise by forming a pitch between the circumferential air-gap centers of the adjacent slot opening portions non-uniformly, thereby reducing higher order components of the magnetomotive force harmonic frequencies of the stator which cause electromagnetic noise.
In order to achieve the above object, according to one aspect of the present invention, there is provided an alternator including:
a stator having an annular stator core provided with a number of slots extending axially disposed in lines circumferentially so as to open on an inner circumferential side and a stator coil wound into the stator core so as to be installed in the slots;
a rotor having a number of claw-shaped magnetic poles for alternately forming north-seeking (N) and south-seeking (S) poles about a rotational circumference, the rotor being rotatably disposed on the inner circumferential side of the stator core;
a bracket supporting the rotor and the stator; and
a rectifier disposed at a first axial end of the stator and connected to end portions of the stator coil, the rectifier converting alternating current from the stator coil into direct current,
wherein a number of slots is two per phase per pole; and
the stator coil comprises a number of winding sub-portions in each of which a long strand of wire is wound so as to alternately occupy an inner layer and an outer layer in a slot depth direction within the slots at intervals of a predetermined number of slots by folding back the strand of wire outside the slots at axial end surfaces of the stator core.